Many very different types of such devices are in existence. For example, in the Italian Patent 1070935 (BLUM) a description is given of hooks, which can be rotated between a retracted position and an extended position into the lateral wall of holes, for fastening a hinge.
The Italian Patent 1060626 (Heinze) describes locking elements which comprise a shaft, suitable for being rotated around its own axis, with one projecting part, suitable for gripping the walls of a hole, for fixing; the projecting part is flat, at right angles to the shaft, and is disc-shaped, elliptical or in the shape of a flat spiral. Such a locking element cannot be used when inserted into a hole which is coaxial with the element, but can only function if it is positioned with its axis oblique with respect to the wall of the hole, or if it is inserted out-of-alignment in a hole which has a much bigger diameter. In addition, it does not allow gradual gripping, and all of this causes its application to be considerably limited.